The invention relates to a venting system for hydraulic systems.
A bleeder valve for venting gases from a hydraulic system is already known. The bleeder valve has a valve body with two valve chambers, which are connected with each other by a bore, one of which has a narrowed inlet connected with the hollow chamber of the hydraulic system, and a valve seat with a first ball as the valve body assigned to the bore. A valve body is located in the first valve chamber, which is pushed away from the valve seat by its own weight and has a greater inherent weight than the hydraulic liquid. The second valve chamber contains a valve seat assigned to the bore with a second ball, prestressed by a spring, as the valve body, and has an opening towards the outside air. When the pressure in the system exceeds a predetermined value, the second ball is raised so that the air escapes (DE 92 12 977 A1).
It is furthermore known to detect impurities in hydraulic systems by means of an optical sensor (DE Mag.: "fluid", November 1991, pp. 24 to 26).
Finally, it is known to employ a light source and a light receiver for detecting gas (DE 29 05 079 A1).
Because of the separation of gasses dissolved in the liquid or because of leakage, gases can collect in some places in hydraulic systems, which possibly constitute an obstacle for operating the devices which are part of the system or for their way of functioning. Care is taken for this reason that no large air or gas volumes can form in certain locations, or respectively can increase to a size which interferes with the operation of the system. Bleeder valves can be installed at the locations in a system where such gases can collect which, when the gas volume has reached a defined size, open a conduit to a space into which the gas can escape. In most cases the bleeder valves open to the outside air. With a bleeder valve open, the hydraulic liquid displaces the gas. In this case it is necessary to prevent the hydraulic liquid, which is under pressure, from escaping through the open bleeder valve.